In known folding devices which are used to produce folded printed products from a web of printed material (usually paper) the different folds are produced in the course of a series of successive exchanges between various cylinders, the axes of which are parallel.
First, the web of material is folded lengthwise by a folding device forming in the web a continuous fold parallel to the two edges of the web. Next, the folded web is cut transversely into printed products between a cutting cylinder having external cutting blades disposed along its generatrices and a transfer cylinder having on its outer surface rubber cutting counter parts which cooperate with the cutting blades. Impaling pins on the transfer cylinder penetrate the leading edge of the printed product thus cut in order to support it on the transfer cylinder for further processing.
The printed products then receive a first transverse fold between the transfer cylinder and a folding cylinder. In order to form this first fold, an engaging blade placed on the transfer cylinder acts at the middle of the printed product to be folded so as to insert this printed product into a folding jaw provided on the outer surface of the folding cylinder along a generatrix. If an additional fold must be made perpendicular to the first fold formed by the cylinders, and consequently parallel to the fold formed by the first folding device, the printed product already folded is transferred to a chopper fold device.
Sometimes, however, it is desired to make a second fold parallel to the first transverse fold. In this case, the above mentioned folding cylinder is provided with a second folding jaw disposed on its outer surface, along another generatrix offset from the first folding jaw by a circle arc of length equal to a quarter of the length of the printed product to be folded, so that the second jaw is disposed behind the first jaw with respect to the direction of rotation of the folding cylinder. A second cylinder parallel to the first folding cylinder interacts with the first folding cylinder to form a second transverse fold in the printed product. The second folding cylinder comprises a prehensile gripper which grips the dorsal part of the first transverse fold in the first folding jaw of the first folding cylinder and an engaging blade which produces the second transverse fold by inserting the printed product into the second jaw for forming a second fold which is supported by the first folding cylinder.
Sometimes a folding device of this latter type is used to form a printed product having a folded length equal to one third of the printed product's unfolded length. In this case, the relative positions of the various folding jaws and engaging blades are modified on the folding cylinders so as to occupy positions corresponding to one third and two thirds of the length of the printed product to be folded.
In order for known folding devices to alternate between a configuration for forming a single transverse fold and a configuration for forming two transverse folds, the second folding cylinder for forming the second transverse fold is mounted in journal bearings eccentric to the axis of the first folding cylinder, so that the second folding cylinder can be activated and deactivated.
In the configuration for producing a single transverse fold, the second cylinder is deactivated so that the center-to-center distance between the first folding cylinder and the second folding cylinder is increased so as to produce an uncoupling of this second folding cylinder with the first folding cylinder. As a result of this uncoupling, the second folding cylinder is immobilized so as to be held in a fixed position in which the grippers and the engaging blade of the second folding cylinder are inactive and do not interfere with the operation of the first folding cylinder. Furthermore, when the folding device is in this configuration, it is necessary to modify the release position of the printed product folded by the first folding jaw, by adjusting the eccentric cam controlling the opening of the first folding jaw on the first folding cylinder. The second folding jaw is opened and closed in continuous manner on the first folding cylinder but this movement performs no function because the engaging blade designed to insert the printed product into the second jaw does not operate.
When changing from the configuration of the folding device operating to produce a second transverse fold to the configuration operating to produce a single transverse fold, it is also necessary to secure onto the chassis on which the folding cylinders are mounted, a printed product guide between the immobilized second folding cylinder and the first folding cylinder. This guide prevents the end of the folded printed product from butting against the second folding cylinder and thus from being subjected to tearing or wrinkling.
As apparent from the above description, the modification of known folding devices from one folding configuration to another folding configuration is time consuming and necessarily must be carried out manually.